Is it possible that the board is having issues with some sort of overheating ?

That's most unlikely. Unless you are using very old firmware, the firmware will warn you if any of the internal stepper drivers report an over-temperature condition, about 20C before they shut down because of over-temperature.

Also, your prints don't show any layer shifts, which is what you would get if the stepper drivers reached the shutdown temperature.

You can monitor the CPU temperature in Duet Web Control.

Your two prints look very similar to me, so I think the artefacts in them are probably caused by the slicer.

What architecture is the printer? Also, what is the pitch of the wobbling pattern along the long straight wall?

That looks like too high bed temperature. Did you check the thermistor there? What is the displayed temp? Do you have an IR thermometer or another way to measure the bed temp and crosscheck with what Duet says?

That looks like too high bed temperature. Did you check the thermistor there? What is the displayed temp? Do you have an IR thermometer or another way to measure the bed temp and crosscheck with what Duet says?

No, it’s not a bed temp issue.
Setting is 55° C, actual on the Duet is 55,7°C. Reading with an IR thermometer is 53,2°C

BTW the height of the part is 11,69mm instead of 10. Nothing to do with bed temp.
The build plate lowered by an additional 1,69 mm than it should.

From one of your photos, it looks like your bed moves in the Z direction. Are you using Z lift in your retraction settings? if so then it's possible that your Z acceleration (or just possible maximum speed or jerk) is set too high, causing the Z axis to lose steps when lifting the bed (e.g. undoing Z lift) but not when lowering the bed. If that's the reason, reducing Z acceleration or increasing motor current may fix it.

To test this theory, trying setting the bed a measured distance below the nozzle (maybe just touching it), then repeatedly do Z+5 followed by Z-5 many times. Then see whether the bed height is the same as it was originally.